confused

In article <SLEHAR.91Aug3103428 at park.bu.edu>, slehar at park.bu.edu (Steve Lehar) writes:
>> Feedback: For years it was a mystery why the pathway from the lateral
> geniculate nucleus (first stage in the visual pathway) to the primary
> visual cortex (second stage) is actually SMALLER than a reciprocal
> pathway from visual cortex BACK to the lateral geniculate! Indeed
> throughout the brain we see multiple feedback pathways. What is the
> significance of these backwards connections? Grossberg proposes that
> the feedback allows for a resonant matching between lower level and
> higher level representations. At each level of representation (within
Do you have any references on a functional significance for backprojections
in the visual cortex? I believe to neurophysiologists there is still a
great deal of mystery as to their functional significance. I am not
familiar with the Grossberg model, but do you have any references from
the neuroscience literature? I know people have looked at cooling
area V2 and examining its modulatory on V1. The result was inconclusive -
the greatest change being in the infragranular layers of V1 (response of V1
neurons increased with V2 being cooled and some neurons that were
directionally selective in one direction became responsive to movement
in both directions). In the supragranular layers of V1 the affect was
mostly to turn of the cell. All together I believe only 1/3 of neurons
were affected.
> each neural layer) there are certain computational constraints that
> are expressed within that layer by excitatory or inhibitory
> interactions. For simple cells in visual cortex, for instance, an
> edge found at one location at, say, 30 degrees, is inconsistant with
> an edge found at that SAME location but a different orientation, say
> 60 degrees. The cells that represent these conflicting
> representations experience a mutually inhibitory relationship so that
> only one can remain active even when both receive some stimulation.
Why is it inconsistent to have 2 lines of different orientations at a
point? The visual scene is filled with such examples.
Thomas